'Based on our findings, we believe that microarray will and should replace karyotyping as the standard for evaluating chromosomal abnormalities in fetuses', said Professor Ronald Wapner, lead author of the study at Columbia University Medical Center, USA.

The researchers analysed fetal DNA isolated from 4,400 mothers who underwent amniocentesis or chorionic villus sampling. The women selected were either older mothers or those whose fetuses showed signs of developmental abnormalities from initial ultrasound screening. The fetal DNA samples were split in two, with one half being sent for chromosomal microarray testing and the other for standard karyotyping.

Professor Wapner told Bloomberg Businessweek: 'The biggest advantage of microarray is it can give us a lot more information. We are expanding the information a person can get out of prenatal testing, identifying additional and more serious problems'.

Karyotyping looks at the overall shape of the chromosomes, looking for obvious physical defects. However chromosomal microarray tests look at the DNA sequence to find mutations that could be harmful.

Researchers found in six percent of cases where suspect structural changes were detected via ultrasound but karyoptying was normal, the microarray tests were able to pick up genetic defects that might explain these changes. 'This allows us to better counsel a patient', remarked Professor Wapner to Bloomberg Businessweek.

In a separate study, led by researchers at the National Institute of Child Health and Human Development, Maryland, USA, this technology was used to investigate potential genetic causes for stillbirth. Karyotyping identified the cause for stillbirth in 71 percent of cases, while chromosomal microarray technology achieved this in 87 percent of cases.

Although microarray technology can produce more genetic information than karyotyping, it costs up three times more to administer. The significance of the genetic data is also not always understood.

'These reports highlight the power and complexity, and some of the pitfalls, of using new genomic technology in clinical practice', wrote Dr Lorraine Dugoff, from the Hospital of the University of Pennsylvania, in an editorial published alongside the studies.

Currently chromosomal microarray testing requires an invasive procedure, with a small risk of a miscarriage, to isolate the fetal DNA, making it unlikely to be offered as standard care for pregnant women. However techniques are now being developed to isolate fetal DNA from maternal blood samples (see BioNews 683).

'We hope that in the future - when microarray can be done non-invasively - every woman who wishes will be offered microarray, so that she can have as complete information as possible about her pregnancy', said Professor Wapner.

The effectiveness of a prenatal test for Down syndrome has been thrown into doubt after its developers, Sequenom, admitted that study data had been 'mishandled' by its employees. The company, which had been producing apparently strong results in house for its DNA and RNA blood testing products...

By Evelyn Harvey: A new method for early detection of genetic diseases in unborn babies using a simple blood test can detect the inherited condition beta-thalassemia, according to a study published in Proceedings of the National Academy of Sciences. Although the technique, which analyses cell free fetal DNA (cffDNA) present...

Scientists at Stanford University in California, US have developed a new non-invasive prenatal test for Down's syndrome. Stephen Quake and colleagues successfully identified presence and absence of fetal chromosomal abnormality in 18 pregnant women from maternal blood samples. The work is published this month in the journal...